The bridge is made of hot gas, and connects two galaxy clusters across 10 million light-years of intergalactic space, the ESA said:

"In the early Universe, filaments of gaseous matter pervaded the cosmos in a giant web, with clusters eventually forming in the densest nodes," the agency explained.

"Much of this tenuous, filamentary gas remains undetected, but astronomers expect that it could most likely be found between interacting galaxy clusters, where the filaments are compressed and heated up, making them easier to spot.

"Planck's discovery of a bridge of hot gas connecting the clusters Abell 399 and Abell 401, each containing hundreds of galaxies, represents one such opportunity."

The temperature inside the cloud is thought to be more than 80 million degrees C. Scientists will now examine the cloud further, in an attempt to discover more about the structure of the universe.

The primary role of the Planck mission is to examine ancient light in the deep corners of space.

When background microwave radiation interacts with hot gas in space, it creates a unique form of energy distribution known as the Sunyaev-Zel'dovich effect. It is this effect which enabled astronomers to find the bridge between Abell 399 and Abell 401.

"Planck is helping to reveal hidden material between galaxy clusters that we couldn't see clearly before," said James Bartlett of Nasa's Jet Propulsion Laboratory.